Compression relief type engine brakes which enable an engine to operate in a braking mode are well known. In the braking mode the engine operates essentially as an air compressor to provide a retarding horsepower to brake the vehicle. The basic compression relief brake shown in U.S. Pat. No. 3,220,392 (Cummins) comprises a master piston and a slave piston interconnected by a closeable hydraulic circuit so that when the master piston ascends the slave piston descends. The slave piston, which has a push actuation connection to an exhaust valve of the engine, has an upward position in which the exhaust valve is retracted or a downward position in which the exhaust valve is caused to open. The master piston is moved upwardly by an engine cam or other member which has a proper lift timing to lift the master piston at the appropriate time in the engine cycle. Typically the exhaust valve is opened by the master piston near the end of the compression stroke so that the pressure which has built up in the engine cylinder is released to the atmosphere and is not recovered during the power stroke.
Various modifications have been made to the basic compression relief brake.
A compression relief type brake manufactured by Jacobs Manufacturing Co. adapted to be installed in a Caterpillar 3406B diesel truck engine is known and is discussed more fully under Description of the Preferred Embodiment below. A timing cam is selected in a manner to make the exhaust valve open and retract promptly before commencement of the normal opening of the exhaust valve which comes near the end of the power stroke, this prompt retracting helping to reduce strain and wear.
However, such a timing cam that offers prompt closing of the exhaust valve is unavailable in many other engine models. In the absence of a prompt closing cam, to gain prompt closing of the exhaust valve brakes have used pin valves and reset valves associated with the slave piston.
For example, U.S. Pat. No. 4,423,712 (Mayne et al) provides a reset mechanism above the slave piston. The main components of the reset mechanism (FIG. 2a) include a moveable spool 110, and a port 108 in the top of a slave piston 50', the port 108 leading to an accumulator housed internally in the slave piston 50'. The spool 110 is mounted to slide up and down in a mount above the slave piston 50'. The spool 110 has an upward position pictured in FIG. 2a and a maximum downward position seen in FIG. 2b. In the maximum downward position an enlarged top 110a of the spool 110 catches on shoulders of the mount so that the spool 110 will descend no further. In operation, when the slave piston 50' descends hydraulic pressures in the upper circuit also cause the spool 110 to descend to cover the port 108. But when the spool 110 reaches its maximum downward position of FIG. 2b the port 18 becomes uncovered as seen FIG. 2c so that fluid flows through the port 108 into the accumulator causing the slave piston 50' to retract which causes the exhaust valve to retract, which provides the prompt closing action of the exhaust valve.
U.S. Pat. No. 4,399,787 (Cavanaugh) shows a pin valve mechanism. The patent is directed at returning the exhaust valve 60 upwardly to its neutral position promptly prior to the normal opening of the exhaust valve 60. To accomplish this quick closing, the pin valve is provided in a mount above the slave piston 50. The pin valve moves up responsive to the level of gas pressure in the engine cylinder, the pin valve being sensitive to an upper duct 40's fluid pressure which is made to depend on the cylinder's gas pressure. After the slave piston 50 initially descends to open the exhaust valve 60, gases escape from the engine cylinder causing the gas pressure in the cylinder to drop which acts to cause the pin valve to ascend which shunts hydraulic fluid out of the upper duct 40 which causes the slave piston 50 to go up which causes the exhaust valve 60 to close. The specific construction and operation of the pin valve mechanism are given in Col. 5, line 61 to Col. 7, line 41.
U.S. Pat. No. 4,648,365 (Bostelman) shows a reset mechanism associated with the slave piston.
U.S. Pat. No. 3,405,699 (Laas) shows a trip valve mechanism associated with a slave piston to limit the total allowable travel of the slave piston and thus prevent damage to the engine. The components include a trip-valve 29 shaped like a cup and a spill hole 35 formed in the top of the slave piston. In brake operation, normally the trip valve 29 covers the spill hole 35 and remains seated due to a spring 31 and due to fluid pressures above the valve 29. However, when the slave piston travels too far downwardly a flange at 32 on the top of the valve 29 catches, so that the spill hole 35 uncovers and the hydraulic system is unloaded through the spill hole 35.
U.S. Pat. No. 4,706,625 (Meistrick et al) shows another brake which senses force required to hold open an exhaust valve during a compression release event and then releases the hydraulic pressure when this force is decreased substantially, thereby causing the exhaust valve to close. In this case a reset valve 106 uncovers a duct 146 which vents fluid from the high pressure circuit to the low pressure circuit.
Other patents of interest include the following:
U.S. Pat. No. 4,150,640 (Egan) shows a fluid pressure control valve 76 in an upper fluid circuit 26 which relieves fluid pressure when the fluid pressure exceeds a predetermined minimum, whereby the risk of damage to the injector push rod 32 and other components is reduced.
U.S. Pat. No. 3,859,970 (Dreisin) shows another form of compression relief brake.
U.S. Pat. No. 4,271,796 (Sickler et al) shows a ball type pressure relief valve fitted internally in the master piston which acts to relieve excess pressure in the high pressure circuit.
U.S. Pat. No. 4,251,051 (Quenneville et al) shows a solenoid valve useable in a brake.
U.S. Pat. No. 4,898,128 and U.S. Pat. No. 4,655,178 both by Meneely show anti-lash adjusters for compression relief brakes.